Field of the Invention
The present invention relates to a measurement apparatus and method of a mobile communication system and, in particular, to a measurement apparatus and method for communication of a low mobility device.
Description of the Related Art
Mobile communication systems have developed to provide the subscribers with voice communication services on the move. With the advance of technologies, the mobile communications have been evolved to support high speed data communication services as well as the standard voice communication services. Recently, as one of the next generation Universal Mobile Telecommunication System (UMTS) mobile communication system, Long Term Evolution (LTE) is on the standardization by the 3rd Generation Partnership Project (3GPP). LTE is a technology designed to provide high speed packet-based communication of up to 100 Mbps higher than the data rate of the legacy system.
Meanwhile, many discussions are being conducted for providing diverse services in the UMTS/LTE mobile communication system. M2M/MTC is one of the representative technologies under discussion. Machine To Machine/Machine Type Communication (M2M/MTC) denotes the communication between electronic devices or between electronic device and data server through a mobile communication network. The M2M/MTC technology is applicable to the automotive telematics, logistics management, intelligent metering system, remote asset management system, Point-Of-Sale (POS), and security-related field. The M2M/MTC device (e.g. metering system) is likely to have low mobility as compared to the normal mobile phone. There is therefore a need of modifying the procedures specified for the normal mobile phones operating in the mobile communication system.
FIG. 1 is a diagram illustrating a structure of a 3GPP UMTS mobile communication system.
Referring to FIG. 1, the User Equipment (UE) 101 is a terminal or a subscriber connected to a Node B (NB) 105 through a radio link to participate in radio communication. The NBs 105, 110, 115, 120, 125, or 130 are the radio base station apparatuses directly responsible for communication with UEs and manage the corresponding cells. The Radio Network Controllers (RNCs) 140 and 150 control the NBs and radio resources. The RNCs 140 and 145 connect to the Packet Switched or Packet Service (PS) network via the Serving GPRS Support Node (SGSN) 150. The RNCs 140 and 145 and SGSN 150 are connected through lu-PS interface and exchange packet-switched control signal. The SGSN 150 is responsible for various control functions and mobility management for the idle mode terminals. The SGSN 150 is also responsible for the data related to the subscriber's service billing and controls communication to exchange data with the UE 101 through the Serving RNC (SRNC) of the UE 101. The Serving Gateway (S-GW) 160 is the apparatus for providing data bearer and allocates and releases the data bearer under the control of the SGSN 150.
FIG. 2 is a diagram illustrating a structure of the 3GPP LTE mobile communication system.
Referring to FIG. 2, the radio access network of the LTE mobile communication system includes Evolved Node Bs (eNB or Node B) 205, 210, 215, and 220; Mobility Management Entity (MME) 225; and Serving Gateway (S-GW) 230. The User Equipment (UE) 235 connects to an external network through the eNB 205 and S-GW 230. Each of the eNBs 205 corresponds to an entity combining the legacy Node B and RNC of the UMTS system. The UE 235 connects to one of the eNBs 205 to 220 through a radio channel and each eNB is responsible for the complicated functions as compared to the legacy Node B. In LTE, since all user traffics including the traffic of real time service such as Voice over IP (VoIP) are served through a shared channel, there is a need of a device for collecting the status information of the UEs to schedule the UEs, and the eNBs 205 to 220 are responsible for this function. The eNBs 205 to 220 are also responsible for controlling radio resource of the corresponding cells. Typically, an eNB controls plural cells. In order to secure the data rate of up to 100 Mbps, LTE adopts Orthogonal Frequency Division Multiplexing (OFDM) as radio access technology on the 20 Mhz bandwidth. LTE also adopts Adaptive Modulation and Coding (AMC) for determining the modulation and channel coding rate in adaptation to the channel condition of the UE. The S-GW 230 is the entity for providing data bearers so as to establish or release data bearer under the control of the MME 225. The MME 225 is the entity responsible for various control functions and mobility management of the idle mode UEs, in connection with the eNBs.
FIGS. 3a to 3c are diagrams illustrating the idle mode UE management method in the 3GPP UMTS/LTE mobile communication system.
Referring to FIGS. 3a to 3c, reference number 301 of FIG. 3a denotes a legacy UE such as mobile phone, reference number 302 denotes an eNB of the LTE mobile communication system, and reference number 303 denotes an RNC of the UMTS mobile communication system. In FIG. 3a, reference numbers 311 and 313 denote signaling RNC/eNB-related information for supporting efficient management of the legacy idle mode UEs in the UMTS/LTE mobile communication system. Reference numbers 321 to 327 of FIG. 3b denote details of measurement method of the legacy UE in the UMTS mobile communication system, and reference number 331 to 335 of FIG. 3c denote details of the measurement method of the legacy UE in the LTE/UMTS mobile communication system. The measurement method denoted by reference numbers 331 to 335 of FIG. 3c can be applied to the UMTS mobile communication system as well as the LTE mobile communication system, and the UMTS system signals the indication information indicating whether the measurement method denoted by reference numbers 321 to 327 or the measurement method denoted by reference numbers 331 to 335 is applied and configuration information related thereto.
In the UMTS mobile communication system, the RNC configures the informations for supporting the measurement of the legacy idle mode UEs into system information and broadcasts the system information within the cell. Here, the idle mode UE denotes the UE having no Radio Resource Control (RRC) connection with the RNC. In the UMTS mobile communication system, such informations include Sintrasearch, Sintersearch, SsearchRATm, Sprioritysearch1, and Sprioritysearch2. The roles of these informations are described with reference to reference numbers 321 to 327 of FIG. 3b and reference numbers 331 to 335 of FIG. 3c. 
In the LTE mobile communication system, the eNB configures the informations for supporting the measurement of the legacy idle mode UE into the system information and broadcasts the system information within the cell at step 313. Here, the idle mode UE means the UE having no RRC connection with the eNB. The system information of the LTE mobile communication system is capable of including Sintrasearch and Snonintrasearch informations. The roles of these informations are described with reference to reference numbers 331 to 335 of FIG. 3c. 
Upon receipt of the system information, the idle mode UE of the UMTS mobile communication system performs the measurement procedure 321 to 327 or 331 to 335. The UMTS system information includes the information indicating the measurement operation to be executed. If it is indicated to execute the UE measurement procedure of steps 321 to 327, the system information includes Sintrasearch, Sintersearch, and SsearchRATm informations. If these informations are received in the system information, the idle mode UE of the UMTS mobile communication system compares the measurement value of the radio signal of the current serving cells with the reference threshold values received in the system information. The measurement value of the radio strength of the serving cell can be the value of the received signal power to the serving cell's reference channel or LTE mobile communication system's Reference Signal (RS) or the value of the received quality of the reference channel of the serving cell to the entire interference. Here, the reference channel can be Common Pilot Channel (CPICH) of the UMTS system and Reference Signal (RS) of the LTE system. Also, the received signal power of the reference channel of the serving cell as the measurement can be Received Signal Code Power (RSCP) of the UMTS system and the Reference Signal Received Power (RSRP) of the LTE system. Also, as an example of the measurement, the received signal quality of the serving cell's reference channel to the entire interference is Ec/No of the UMTS system and Reference Signal Received Quality (RSRQ) of the LTE system. The CPICH RSCP/CPICH Ec/No or RSRP/RSCP of the UMTS mobile communication system and LTE mobile communication system are specified in the 3GPP standard TS25.2151TS36.214.
The radio signal strength measurement value of the serving cell can be measured as the reference channel received power of the serving cell or the received signal quality of the serving cell's reference channel to the entire interference, and the two measurements can be signaled as specific values. For example, the when using the RSCP measurement value of the reference channel of UMTS, the measurement value can be signaled as Sintrasearch1, Sintersearch2, and SsearchRATm1 values; and when using the Ec/No measurement value of the reference channel, the measurement value can be signaled as Sintrasearch, Sintersearch, and SsearchRATm.
If the Sx of the current serving cell is (equal to or) greater than the Sintrasearch value as denoted by reference number 321 of FIG. 3b, the idle mode UE of the UMTS mobile communication system skips the intra-frequency (herein after the term “Intra-F” is used interchangeably) measurement process and, otherwise if the Sx of the current serving cell is (equal to or) less than the Sintrasearch value as denoted by reference numbers 323, 325, and 327, performs the intra-frequency measurement process. Also, if the Sx of the current serving cell is (equal to or) greater than the Sintersearch value as denoted by reference number 321 and 323, the idle mode UE skips the inter-Frequency (hereinafter, the term ‘Inter-F’ is used interchangeably) measurement process and, otherwise if Sx of the current serving cell is (equal to or) less than the Sintersearch value as denoted by reference numbers 325 and 327, performs the inter-Frequency measurement. Furthermore, if Sx of the current serving cell is (equal to or) greater than SsearchRATm value of a specific system m as denoted by reference numbers 321, 323, and 325, the idle mode UE skips Inter-Radio Access Technology (hereinafter, the term ‘Inter-RAT’ is used interchangeably) measurement process and, otherwise if Sx of the current cell is (equal to or) less than SsearchRATm as denoted by reference number 327, performs the inter-RAT measurement process to the specific system m.
The LTE and some UMTS mobile communication systems adopt priority concept to frequency/system in order for the idle mode UE to perform the measurement and cell (re)selection in consideration of the priorities assigned to the frequencies/systems. Suppose that the current serving cell of the idle mode UE operates on frequency 2 with priority 2 and neighbor cells operate on frequency 1 with priority 1 and frequency 3 with priority 3. In this case, although the radio signal strength of the current serving cells is advantageous, the UE performs the inter-frequency measurement to the frequency 3 having the high priority as compared to the current serving cell's and, if a neighbor cell having the channel quality greater than a predetermined threshold value on the frequency 3, performs cell re(selection) on the frequency 3 and, if the radio signal strength of the current serving cell is advantageous, it is not necessary to perform the inter-frequency measurement on the frequency 1 having the low priority as compared to the frequency of the current serving cell. However, if the radio signal strength of the current serving cell falls below the threshold value, it becomes necessary for the UE to perform inter-frequency measurement on the frequency 1 and, if a neighbor cell having the radio signal strength greater than the threshold value on the frequency 1, performs cell (re)selection on the frequency 1.
Reference numbers 331 to 335 of FIG. 3c denote a measurement process of the idle mode UE in the UMTS mobile communication system and LTE mobile communication system adopting the frequency/system priority concept. If Sx of the current serving cell is (equal to or) greater than Sintrasearch value as denoted by reference number 331, the idle mode UE skips intra-frequency measurement and, otherwise if Sx of the current serving cell is (equal to or) less than Sintrasearch value as denoted by reference numbers 333 and 335, performs the intra-frequency measurement. Also, if Sx of the current cell is (equal to or) greater than Snonintrasearch (LTE) or Sprioritysearch1/Sprioritysearch2 (UMTS) as denoted by reference numbers 331 and 335, the idle mode UE skips inter-frequency/inter-RAT measurement process to the frequency/system having the priority equal to or less than that of the frequency of the current serving cell. If Sx of the current serving cell is (equal to or) less than Snonintrasearch (LTE) or Sprioritysearch1/Sprioritysearch2 (UMTS) as denoted by reference number 335, the idle mode UE performs inter-frequency/inter-RAT measurement process to the frequency/system having the priority to the frequency/system having the priority equal to or less than that of the frequency of the current serving cell.
However, the above-described measurement method is inefficient for the idle mode M2M/MTC device with low or no mobility. That is to say, it is inefficient to apply the measurement method designed for the legacy UE such as mobile phone having relatively high mobility to the idle mode M2M/MTC device having low mobility. This is because the conventional measurement method makes the M2M/MTC device perform measurement operation unnecessarily even though no movement is predicted. There is therefore a need of an efficient measurement method for the idle mode M2M/MTC device with low mobility.